Thursday, January 29, 2009

Wheel test

When I carried the boxes up the stairs, I honestly contemplated that they might be empty. Of course, they weren't. It's just that these wheels are sicko light. Cycling Technology's Mt Washington wheels, assembled by Nico Toutenhoofd, checked in at an insane 776 grams for the pair. This is 5 grams lighter than the claimed mass for the super-pricey (okay, still cheaper than my wheels) Mavic R-Sys Premium, the rear wheel alone. Yet as impressive as the number is, it's nothing compared to the impression one gets from lifting the thing. Even with my Red 11-23 cassette, the glued-on Veloflex Record Carbon tire, and valve extenders, these wheels tip the scale at 1390 grams, just 30 grams less than the R-Sys without tires, tubes, or cassette. Sick. And that's going generous with the glue.

Combined with my Lightning SL crankset (170mm, 110mm BCD, 129 gram SRAM Rival/Force chainrings, 9.7 gram Shimano chainring bolts, 580.8 grams total with bearings), when things settled down after I loaded my bike, including Speedplay X/1 pedals and a Ti bottle cage, the LCD was reading a svelte 5360 grams. Sure, hardly competitive with Gunther Mai's 2970 gram work of weight weenie genius, but still close to a kilo and a half below the UCI limit. And my bike is designed to go fast, reliably, at a price competitive with top-end stock bikes, not chase the grams-at-any-cost mission of true weight weenies. Don't race what you're unwilling to crash. Okay, at more than $2k, I'm not excited about the idea of crashing these wheels. But still they're well under the $5k+ for a pair of top-end Lightweights or Lews, let alone the $15k custom Lightweights on Gunther's Spin. Less then the wheels I saw a junior girl riding at a recent 'cross race.

The Fuji SL/1 with new Mt Washington wheels and Lightning crankset

Obviously, when the last of my four coats of glue had dried (three on the rims, one on the tire), I was excited to give 'em a shake-down spin. So flaunting Murphy, I rode the bike to Caltrain to load on the bike car for my commute from San Francisco to Palo Alto. Luck was on my side: nobody jammed their pedal into my spokes.

A few early hic-cups. There seemed to initially be an issue with the palls on the freehub of the Extralite rear hub engaging, but these settled down. then I was getting a weird pinging sound, until I finally realized the KCNC skewer on my front wheel needed to be tightened (these skewers need to be tightened down a bit more than typical skewers). Everything was fine, then. The wheels just scream "climb fast", especially when combined with the super-low rolling resistance (measured by Al Morrison) Veloflex Record tires.

Of course, I know better. Even a pound saved off the bike, wheels or anywhere else, isn't worth more than 10 seconds out of close to 20 minutes up Old La Honda Road. Day to day variations in wind are a bigger factor. So many things can yield 10 second differences. This sort of advantage, while significant, is imperceptible. Indeed, I assert I could hide a full kilogram in your bottom bracket and, if it fit, you wouldn't notice until you lifted the bike. Weight reduction is a game of advantages seen only by the stopwatch. Yet in racing, small advantages can result in big differences a small number of times. And we who lack in talent need to take advantage of every chance we get.

Back to the ride: the Monday Noon Ride has only modest climbing, as the pack rides around Portola Valley and Woodside. The wind was blowing, and I immediately noticed in cross-winds that front wheel felt jittery. At under 55 kg, I get blown around fairly easily. Gutter-fests aren't my cup. This was a bit annoying, but not a real safety concern. In cross-winds, these aren't the wheels of choice anyway, since it's repeatedly been shown in wind-tunnel testing that deeper dish wheels have the greatest advantage at non-zero yaw angle (for example, see Hed's data). Yaw equals cross-wind.

Ironically, on this Noon Ride I was dropped on the main climb, up Sand Hill road. Someone up ahead let a gap open, and I was stuck in a laughing group. Snooze = lose. Bike racing, or faux racing like the Nooner, is like that...

Close-up of the rear wheel. Note the semi-triangular rim profile.

On Wednesdays, the Noon Crew climbs classic Old La Honda Road. I couldn't resist the temptation to deliver the wheels to their element. I was still under the weather from recent illness, plus substantially training-deprived with barely any extended climbing during the preceding 5 weeks (only a single day in Laos), so I knew I had to pace myself carefully. Luck was on my side on the day, as the truly ballistic climbers were absent or taking it easy, and I managed to be the first to the top, with a decent but not exceptional time of 18:36. Only a minute off my Noon Ride best for last year (still a long way from my 17:03 from 2002). So yeah, the wheels climbed well.

Okay, so a bigger factor was between running and my Laos trip my body weight is lower than it has been in years: body weight can fluctuate a lot more than bike weight can. But every little bit helps. My goal of sub-17 is still looking very, very possible.

But what goes up (usually) must come down. Again there was a bit of a breeze, and rounding the corners on Highway 84, I was more tentative than I should have been due to handling feel. Why were these rims, with only 24 mm depth, behaving so squirrelly? Rim shape? A subtle effect of the Sapin bladed spokes? Narrow 20mm tires? User incompetence? Well, this particular user has never demonstrated great competence on descents, but I suspected something else was at play.

Rim shape is rather unusual on these wheels. The Edge rims are semi-triangular, less rounded than typical "aero" rims. Could this help explain the cross-wind effect? I don't know.

Mac, as always, is unimpressed. He's rather be eating, or maybe getting to know a fuzzy sweater.

Anyway, these wheels are built for climbing, plain and simple. If I am doing a lot of descending, a personal weakness of mine both due to my relative lightness and a general lack of cojones, I want the extra aerodynamic advantage of my Reynolds MV-32 tubular with the superior handling of their Veloflex Carbon tubulars. So I'm not sweating the cross-wind thing. The wheels are great. They even brake okay, with only a bit of modulation from the carbon seam. Not a big deal. The Mount Washingtons are designed for a specific purpose, and designed very well for that purpose. You'll have a hard time coming close to them for less than twice the price.

4 comments:

It was suggested to me on weightweenies that the answer is obvious: light wheels have less inertia, and therefore get blown around easily. Sure, the dish is small, but add in the tire thickness, and it adds up to a decent cross-section far from the axis of rotation, where the exerted torque is maximal. So maybe that's it, although I'd have thought other sources of resistance to rotation dominate. However, it seems a plausible explanation. I suppose I should attach extra mass to the spokes near the rim to test it :).